Card cages are known which comprise a framework within which a plurality of circuit panels or daughter cards are insertable, and within which is disposed a backplane transverse to the back edges of the daughter cards. The upper and lower daughter card edges conventionally are disposed within upper and lower channels defined by the card cage framework and extending to selected positions along the backplane to define the card position within the card cage and to guide the card during insertion into and removal from the card cage. Electrical circuitry of the cards is connected to electrical circuitry of the backplane by any of several types of known connectors and terminals, and is thereby interconnected by the backplane to circuitry of other cards of the array and to other electrical components on the opposite side of the backplane.
Typically each daughter card in present commercial card cages receives all necessary power for its components from the backplane through a plurality of terminals. One typical method involves providing a multilayer backplane having power-carrying circuit paths embedded within it, involving significant fabrication expense, to which terminals are engaged to transmit the power at current levels, ordinarily of about one ampere per terminal, through connectors to the daughter card. Connectors which must house the quite numerous power-carrying terminals also must house signal terminals for the primary purpose of providing signal transmission to and from the daughter cards; signal terminals are thus limited in number and in their position, which in turn limits the capabilities of the daughter cards. Also, the current levels presently available limit the number and types of components usable with the daughter cards.
One approach to distribute power to daughter cards in an improved manner is disclosed in U.S. Pat. No. 4,846,699 in which the power is provided to upper and/or lower edges of each daughter card rather than along the back edge. The upper and/or lower guide channels are defined by elongate electrical connectors containing a plurality of electrical terminals which are movable into and out of engagement with corresponding contact locations along the card by an actuation system within each connector. The plurality of terminals thus distributes electrical power to discrete locations and discrete power circuits on the card. Thus during card insertion and removal the contact sections of the terminals are retracted from the guide channel and would not engage any portions of the card nor interfere with insertion and removal of a card; only when the cards have been fully inserted and locked into position are the terminals moved into electrical engagement with the contact means along the card edge. Examples of such zero insertion force connectors are particularly disclosed in U.S. Pat. No. 4,789,352 and No. 4,834,665. With such connectors, conductors such as flat cables are needed to be routed through the card cage framework above and below the daughter cards and electrically connected to the terminals of the connectors and to a power supply for the card cage.
It is desired to provide a power distribution system for daughter cards of a card cage which utilizes a portion other than the back edge of each card for transmitting power to the card, without interfering with insertion or removal of the card.
It is desired to provide such a system which minimizes the amount of daughter card real estate utilized for receipt and return of power while retaining the benefits attained by a substantial plurality of power connecting sites.
It is additionally desired to provide a power distribution system which electrically connects with the card upon insertion and disconnects upon card withdrawal.
It is also desired to provide such a system which does not require a plurality of cables routed throughout the card cage.
It is further desired to provide such a system which would provide power to each card at substantially increased levels without significant voltage drop.
It is further desired that such a power distribution system not obstruct forced air flow between adjacent daughter cards in the card cage, needed for cooling.